(a) Field of the Invention
The present invention relates to a method for re-ordering multiple layers and detecting signals of which the layers have different modulation orders in a multiple input multiple output antenna system and a receiver using the same. More particularly, the present invention relates to a method for re-ordering layers and detecting signals and a receiver using the same to be able to exert performance approaching a maximum likelihood scheme while having lower complexity than that of the maximum likelihood scheme in a multiple input multiple output (MIMO) antenna system in a form where each layer is modulated and transmitted with different modulation orders.
(b) Description of the Related Art
A wireless communication system of fourth-generation mobile communication needs a high-rate data service of images and packets in addition to an existing audio centered service. In order to meet the above requirement, a multiple input multiple output (MIMO) system using a spatial multiplexing scheme that can perform high-rate data transmission through multiple data stream (hereinafter, “stream” and “layer” have the same meanings) transmission is getting interesting.
In the MIMO system using the spatial multiplexing scheme, data layers each indicating different information are transmitted from each transmission antenna and in a receiving end, the transmitted data layers are separated. Herein, all the layers may be transmitted to a single user and each layer may be transmitted to multiple different users.
A maximum likelihood (ML) signal detecting mechanism, which is a mechanism that finds transmission signal vectors having ML metric values for each of possible combinations of transmission signal vectors in order to detect optimal transmission signals, has been known as the most excellent mechanism until now in view of performance detecting the transmission signals.
However, it is considered that the ML signal detecting mechanism in the related art cannot be substantially implemented since the complexity is exponentially increased as the number of transmission antennas and the number of constellation points are increased.
For this reason, a method for detecting signals such as a linear signal detecting method capable of lowering the complexity, for example, a zero forcing (ZF) scheme and a minimum mean square estimator (MMSE) scheme has been proposed. However, there is a problem in that these linear signal detecting mechanisms are significantly poor in view of performance as compared to the ML scheme.
Meanwhile, as a non-linear signal detecting mechanism, there is a signal detecting mechanism according to an ordered successive interference cancellation (OSIC) scheme that has been known as vertical bell lab layered space time (VBLAST)
Since the OSIC has low system complexity, it can be simply implemented as well as it is excellent in view of performance as compared to the linear signal detecting mechanisms such as ZF, MMSE, etc. However, the OSIC is still poor in view of performance as compared to the ML scheme.
Thereafter, as a signal detecting mechanism approaching the performance of the ML signal detecting mechanism while lowering the complexity of the system, a signal detecting mechanism according to a QR-LRL scheme was proposed.
The signal detecting mechanism according to the QR-LRL scheme re-orders the layers relating to a plurality of streams (e.g., four streams in the case of 4×4 MIMO system), thereby cancelling the interference between signals and detecting received signals.
At this time, the re-ordering of the layers is based on the magnitude of norm values of each column of a channel matrix corresponding to each layer. In other words, it is determined that the larger the norm values of the channel matrix corresponding to the layers, the lower the reliability of the layers becomes.
However, when the plurality of streams have different modulation orders, it is impossible to accurately determine the reliability of the layers only by simply comparing the norm values of the channel matrix corresponding to each layer
Therefore, even when the layers modulated and transmitted with different modulation orders are received by the QR-LRL signal detection mechanism, a need exists for the method for re-ordering layers and detecting signals to be able to accurately determine the reliability of the layers and the receiver using the same
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.